The present invention relates to a photo-electronic device (semiconductor optical module) and a method of producing thereof, particularly to a technology effectively applied to a technology of producing a photo-electronic device capable of preventing breakage of an optical fiber core line comprising a core and a clad and extended in a package and capable of preventing a deterioration in transmission efficiency of light.
There is used a photo-electronic device integrated with a semiconductor laser (semiconductor laser element: semiconductor laser chip) as a light source for an information processing apparatus or a light source for optical communication. As an example of a photo-electronic device, there is disclosed, in Japanese Patent Laid-Open No. 282369/1998 or Japanese Patent Laid-Open No. 307235/1998, an optical communication apparatus (semiconductor laser module) forming a package by a case and a lid (cap) comprising plastics (resin) formed by a transfer mold process, containing a semiconductor laser (laser diode) or a photo detector (photo diode) and extending an optical fiber to inside and outside of the package.
Further, portions of a pad (pad portion) and a lead frame for fixing a silicon substrate, are embedded in the case simultaneously with the transfer mold operation. The silicon substrate is fixed with the semiconductor laser. The optical fiber extended to inside and outside of the package is constructed by a structure in which the optical fiber core line is covered with a cover member up to a middle of the package and a front end thereof is a bare optical fiber at which the optical fiber core line is exposed by removing the cover member. The optical fiber core line is constituted by the core and the clad covering the core and both of them comprise, for example, quartz and are brittle and easy to break by external force.
Further, in the package, the semiconductor laser is covered with transparent gel-like resin comprising silicone resin.
The applicants have investigated to use a copper frame having excellent thermal conductivity (thermal expansion coefficient xcex1=17xc3x9710xe2x88x926/xc2x0 C.) as a lead frame for radiating heat generated at a semiconductor laser element to outside of the package in developing a photo-electronic device integrated with the semiconductor laser.
However, according to the structure, it has been found that exfoliation of an optical fiber is caused by a mounting test by solder reflow (10 seconds at 260xc2x0 C).
In producing a photo-electronic device, a case is formed to embed a portion of a lead frame by transfer mold. A base plate (pad) comprising a copper plate is formed at an inner bottom face of a case and a silicon substrate (thermal expansion xcex1=3.0xc3x9710xe2x88x926/xc2x0 C.) is fixed onto the base plate. A semiconductor laser element, a light receiving element, an optical fiber and the like are fixed onto the silicon substrate. A front end portion of an optical fiber is positioned to face an emitting face of the semiconductor laser element and a front end portion thereof is adhered to the silicon substrate by an adhering agent. Further, a portion at a middle of the optical fiber is fixed to the case by an adhering agent.
Here, the optical fiber indicates also an optical fiber core line formed by a core and quartz covering the core and the optical fiber cable covering the optical fiber core line by a cover member of a jacket. When the optical fiber core line or the optical fiber cable may not be specified particularly or may not preferably be specified, these are referred to simply as optical fiber in the following.
When a constitution of supporting an optical fiber (optical fiber core line) is constructed by two points support constitution of fixing a front end portion of the optical fiber and a middle portion thereof, tensile force is operated to the optical fiber core line by thermal deformation of the base plate caused by heat in the solder mount test and the tensile force exceeds force of adhering the silicon substrate and the optical fiber core line and the optical fiber core line is exfoliated. Exfoliation of the optical fiber at the front end portion of the optical fiber causes a phenomenon in which a deterioration is caused in transmission and reception efficiency of light to and from the semiconductor laser element or light is not inputted at all from the front end.
In order to resolve such a problem, the applicants have investigated to form the lead frame by a material the thermal expansion coefficient of which is proximate to that of silicon. As a material the thermal expansion coefficient is proximate to that of silicon, there are kovar, 42 alloy and the like. Hence, the applicants have formed the lead frame by 42 alloy (xcex1=5xc3x9710xe2x88x926/xc2x0 C.). Therefore, the base plate and the lead integrated to the case are made of 42 alloy. The thermal conductivity of 42 alloy is as small as 13.4 W/mxc2x7k in comparison with 146 W/mxc2x7k of Cu and achieves an effect of capable of restraining temperature rise of the base plate per se and restraining deformation of the base plate. Thereby, there is provided a structure in which the optical fiber is difficult to exfoliate.
Meanwhile, the applicants have investigated also on adaptability of resin constituting the case. Since the case is exposed to high temperature even in a short period of time, as a resin constituting the case, the resin having heat resistant temperature of 200xc2x0 C. or higher has been investigated. Although as resins, there are thermoplastic resin and thermosetting resin, thermoplastic resin is used since thermosetting resin is provided with a drawback in which the time period of molding thereof is long and the resin is not reproducible. Thermoplastic resin is widely used as engineering plastic.
As resin having the heat resistant temperature equal to or higher than 200xc2x0 C., there are polyphenylene sulphide (PPS), polyether sulfone (PES), polyetherketone (PEEK) and liquid crystal polymer (LCP).
PES, PEEK and LCP are expensive and PPS is balanced in view of heat resistance and price.
Although the price is high, the liquid crystal polymer (LCP) is featured in high heat resistance (thermal deformation temperature equal to or higher than 260xc2x0 C.) and high bending strength (bending strength: 21.2 kg/mm2 at 25xc2x0 C.). Further, the liquid crystal polymer is particularly featured in small linear expansion coefficient in a direction of flow of resin in molding thereof. The linear expansion coefficient of the resin in the flow direction is 2.0xc3x9710xe2x88x926/xc2x0 C. and the linear expansion coefficient in a direction orthogonal to the flow is 66xc3x9710xe2x88x926/xc2x0 C.
Hence, the applicants have conceived to prevent breakage caused by the thermal stress of the optical fiber core line by molding the case by making the resin flow in the direction of extending the optical fiber core line and approximating the thermal expansion coefficient of the case in the direction of extending the optical fiber core line to the thermal expansion coefficient of the optical fiber core line.
However, in the case of the liquid crystal polymer, the thermal conductivity is as small as 0.4 W/mxc2x7k and the tensile strength of weld after molding is smaller than 25 MPa in comparison with 55 MPa or more of various engineering plastics. In order to improve the heat radiating performance, the thinner the resin thickness below the base plate fixed with the semiconductor laser element, that is, the thickness of the bottom of the case, the more preferable. However, as mentioned above, the liquid crystal polymer is provided with the low tensile strength of weld and the bottom of the case becomes brittle. Hence, the inventors have conceived to increase the strength by partially thickening the bottom of the case.
Meanwhile, it has been found that there is a case of breaking the optical fiber core line from the following reason by analysis and investigation by the inventors.
FIG. 21 is an enlarged sectional view showing a portion of a package 5 of a photo-electronic device according to an investigation by the applicants. The package 5 comprises a case 10 and a cap 11 adhered and fixed to overlap the case 10.
The case 10 comprises a case main body portion 10a and a slender case guide portion 10b continuous to the case main body portion 10a. The cap 11 comprises a cap main body portion 11a overlapping the case main body portion 10a and a cap guide portion 11b overlapping the case guide portion 10b. 
The case main body 10a is constituted by a box type structure the upper portion of which is opened and is constituted by a structure in which a plurality of leads, not illustrated, constituting external electrode terminals are projected respectively from both sides thereof. A base plate 15 comprising a metal plate is provided at an inner bottom of the case main body portion 10a and a support substrate (silicon platform, not illustrated) is fixed onto the base plate 15.
The support substrate is fixed respectively with a semiconductor laser element, a light receiving element and a front end portion of an optical fiber core line 3a. Further, a gel-like resin 36 is filled in the case main body portion 10a for covering the semiconductor laser element, the light receiving element and the optical fiber core line.
The case guide portion 10b and the cap guide portion 11b are constructed by a structure of guiding an optical fiber cable and an optical fiber core line which becomes bare by removing a jacket (cover member) of the optical fiber cable. That is, match faces of the case guide portion 10b and the cap guide portion 11b are respectively provided with grooves. The grooves comprise cable guide grooves for guiding the optical fiber cable and core line guide grooves 10d and 11d continuous to the cable guide grooves. The cable guide grooves are extended from ends of the case guide portion 10b and the cap guide portion 11b to middle portions thereof and remaining portions constitute the core line guide grooves 10d and 11d. The optical fiber cable is constructed by a structure of covering the optical fiber core line 3a comprising the core and the clad by a cover member (jacket). Therefore, the optical fiber cable integrated to the photo-electronic device is brought into a state of the optical fiber core line 3a by removing the jacket over a predetermined length at the front end side.
The case guide portion 10b and the cap guide portion 11b are inserted with the portion of the optical fiber core line 3a and the portion of the optical fiber cable and the portions are fixed to the case guide portion 10b and the cap guide portion 10b via an adhering agent 38. Further, the front end portion of the optical fiber core line 3a is fixed to the silicon platform via an adhering agent.
It has been found that according to such a structure, there is a case in which optical transmission cannot be carried out by causing a disconnection failure of the optical fiber core line 3a inserted into the case guide portion 10b and the cap guide portion 11b. 
The following has been found as a result of analyzing and investigating the point. That is, in forming the gel-like resin 36, silicone resin having fluidity is supplied to the case main body portion 10a and the silicone resin flows into a clearance between the outer peripheral portion of the optical fiber core line 3a and the core line guide groove 10d. As a result, the gel-like resin 36 and the adhering agent 38 are brought into contact with each other over a long distance in the core line guide groove 10d and 11d. 
The gel-like resin 36 uses the silicone resin and the adhering agent 38 uses epoxy resin of amine species. Further, an adhering agent for fixing the case 10 and the cap 11 also uses the epoxy resin of amine species. The epoxy resin of amine species is used since force thereof of adhering to the plastic case is excellent. However, adhering performance between the gel-like silicone resin and the epoxy resin of amine species or the plastic case is not excellent.
As a result, it has been found that since the optical fiber is not fixed to the case guide portion, there causes a phenomenon in which tensile stress is operated to the optical fiber core line 3a owing to temperature change and the optical fiber core line 3a is broken.
Further, it has been also found that in the case in which moisture is stored at the interface 7, when the photo-electronic device is used in a cold district, there causes a phenomenon in which the moisture stored at the interface constitutes ice and the optical fiber core line is broken by an increase in the volume. The breakage is particularly easy to occur when the interface is disposed at an area of the case guide portion 10b and the cap guide portion 11b. 
It is an object of the invention to provide a photo-electronic device capable of preventing an optical fiber from being broken and a method of producing thereof.
It is other object of the invention to provide a photo-electronic device having high efficiency of optically coupling a photoelectric conversion element and an optical fiber and a method of producing thereof.
It is other object of the invention to provide a photo-electronic device having high heat radiating performance and a method of producing thereof.
The above-described and other objects and novel features of the invention will become apparent from description of the specification and attached drawings.
A simple explanation will be given of an outline of representative aspect of the invention disclosed in the application as follows.
(1) According to an aspect of the invention, there is provided a photo-electronic device including a package having a main body portion containing parts including a photoelectric conversion element at inside thereof and a guide portion a front end of which faces the photoelectric conversion element for guiding, in a penetrated state, an optical fiber for transmitting and receiving light to and from the photoelectric conversion element, in which the optical fiber is fixed to the guide portion by an adhering agent at the guide portion and portions of the main body portion including the photoelectric conversion element and a front end portion of the optical fiber are covered by a protective film formed by a resin transparent to the light and a dam is provided between the protective film and the adhering agent such that the protective film and the adhering agent are not brought into contact with each other.
According to another aspect of the invention, there is provided the photo-electronic device, wherein the package is formed by a case and a cap adhered to overlap the case, the case is formed by a case main body portion and a case guide portion continuous to the case main body portion, the cap is formed by a cap main body portion and a cap guide portion continuous to the cap main body portion, the case main body is portion is embedded with a predetermined shape of a metal plate a portion of which forms a base plate exposed to an inner bottom of the main body portion, remaining portions of which form a plurality of leads extended to inside and outside of the main body portion, a support substrate (silicon substrate: silicon platform) is fixed onto the base plate and the photoelectric conversion element and the optical fiber for transmitting and receiving light to and from the photoelectric conversion element are fixed onto the support base plate.
The support substrate is fixed with a semiconductor laser element, a light receiving element and the front end portion of the optical fiber, the optical fiber is positioned and fixed to input laser beam on one side emitted from the semiconductor laser element from a front end to an inner portion thereof and the light receiving element is positioned and fixed to receive laser beam on other side emitted from the semiconductor laser element. Further, the front end portion of the optical fiber is fixed to the support substrate by an ultraviolet ray cured adhering agent and is fixed to the support substrate by a thermosetting adhering agent.
The protective film is formed by a gel-like resin, the adhering agent is formed by epoxy resin of amine species and the dam is formed by an ultraviolet ray cured adhering agent of epoxy resin species. Further, there is present an air gap at a portion of the main body portion above the protective film.
The metal plate forming the base plate or the leads is formed by 42 alloy or kovar the thermal expansion coefficient of which is proximate to the thermal expansion coefficient of the support substrate or the optical fiber and the case and the cap constituting the package are formed by a resin (liquid crystal polymer) in which the thermal expansion coefficient in the direction along the flow of resin in molding becomes smaller than the thermal expansion coefficient in a direction orthogonal to the flow direction and the case and the cap are molded such that the thermal expansion coefficients in the direction of extending the optical fiber are reduced.
A peripheral edge portion of a bottom of the case main body portion of the case formed by the resin, is projected to thicken more than an inner side portion thereof and at the center of the base plate, the resin is not provided over a predetermined length along the direction of extending the optical fiber and the rear face of the base plate is exposed. The peripheral edge portion of the bottom of the main body portion of the package is projected to thicken more than the inner side portion.
Such a photo-electronic device is produced by the following method.
According to another aspect of the invention, there is provided a method of producing a photo-electronic device in which a package is formed by a case and a cap adhered to overlap the case, the case is formed by a case main body portion and a case guide portion continuous to the case main body portion, the cap is formed by a cap main body portion and a cap guide portion continuous to the cap main body portion, the case main body portion is embedded with a predetermined shape of a metal plate a portion of which forms a base plate exposed to an inner bottom of the case main body portion and remaining portions of which form a plurality of leads extended to inside and outside of the case main body portion, a support substrate (silicon substrate: silicon platform) is fixed onto the base plate, a photoelectric conversion element an electrode of which is connected electrically to the lead is fixed onto the support substrate, an optical fiber is supported by the guide portion in a penetrated state and fixed thereto by an adhering agent, a front end of the optical fiber is fixed to the support substrate to transmit and receive light to and from the photoelectric conversion element and a protective film which is transparent to the light covers the photoelectric conversion element and the optical fiber in the main body portion, the method comprising the steps of fixing the support substrate fixed with the photoelectric conversion element to inside of the main body portion, fixing a front end portion of the optical fiber by an adhering agent, forming the protective film by filling a resin in the main body portion, and fixing the optical fiber to the guide portion by an adhering agent, wherein a dam is formed at a boundary portion of the main body portion and the guide portion such that the protective film does not invade the guide portion prior to forming the protective film.
According to another aspect of the invention, there is provided the method of producing a photo-electronic device wherein a semiconductor laser element is fixed to the support substrate, the front end portion of the optical fiber is positioned and fixed such that laser beam on one side emitted from the semiconductor laser element is inputted from a front end thereof to an inner portion thereof and a light receiving element is positioned and fixed to receive the laser beam on other side emitted from the semiconductor laser element. After optical couple adjustment of the optical fiber, the front end portion of the optical fiber is coupled by the ultraviolet ray cured adhering agent and is fixed thereto by the thermosetting adhering agent.
The case is formed by fastening a lead frame to mold dies of transfer mold and thereafter molding liquid crystal polymer resin to flow from one end portion to other end portion of the case and cutting and removing an unnecessary portion of the lead frame. In the transfer mold, the molding operation is carried out by pressing a portion of the lead frame constituting the base plate to a mold upper die by a pressure pin, the pressure pin is extended over a predetermined length along the direction of extending the optical fiber at the center of the base plate, the flowing resin is divided at one end side of the pressure pin and flows along both sides of the pressure pin and thereafter merges again on other end side of the pressure pin to flow. The case main body portion of the case is molded such that the resin thickness at the peripheral edge of the bottom thereof is thickened. The lead frame is formed by 42 alloy or kovar.
The protective film is formed by a gel-like resin which is transparent to the light, the adhering agent for fixing the optical fiber to the case guide portion is formed by epoxy resin of amine species and the dam is formed by an ultraviolet ray cured adhering agent of epoxy resin species.
According to the means of (1):
(a) Since the dam is present, the silicone resin does not flow out to the case guide portion by riding over the dam. Therefore, the epoxy resin of amine species having poor adhering performance with the silicone resin, is not brought into contact with the silicone resin, the case guide portion is filled with the epoxy resin of amine species, the force of adhering the case and the cap is also maintained and accordingly, the fiber can firmly be fixed, thermal stress caused by thermal variation is difficult to apply to the optical fiber (optical fiber core line), the optical fiber core line is difficult to break and optical transmission failure is difficult to cause.
(b) The thermal expansion coefficient of the case and the cap in the direction of extending the optical fiber is 4.0xc3x9710xe2x88x924/xc2x0 C. (liquid crystal polymer), the thermal expansion coefficient of the base plate comprising 42 alloy is 5xc3x9710xe2x88x926/xc2x0 C., the thermal expansion coefficient of the silicon platform is 3.0xc3x9710xe2x88x926/xc2x0 C., the thermal expansion coefficient of the optical fiber core line is 0.5xc3x9710xe2x88x926/xc2x0 C., all of the coefficients are smaller than that of copper (a=17xc3x9710xe2x88x926/xc2x0 C.) and are provided with numerical values proximate to each other and therefore, it is difficult to cause exfoliation of the optical fiber fixed by the silicon platform and the case guide portion owing to deformation of the base plate. Further, the front end portion of the optical fiber is fixed to the support substrate respectively by the ultraviolet ray cured adhering agent and the thermosetting adhering agent and accordingly, the adhering strength is high and exfoliation of the optical fiber is difficult to cause. As a result, at the front end of the optical fiber, a deterioration in the transmission and reception efficiency of light between the front end and the semiconductor laser element, is not caused and the optical fiber (optical fiber core line) is difficult to break at the case guide portion.
(c) Liquid crystal polymer (LCP) is featured in high thermal resistance (thermal deformation temperature equal to or higher than 260xc2x0 C.) and high bending strength (bending strength: 21.1 kg/mm2 at 25xc2x0 C.), however, the tensile strength of weld after molding is small. Therefore, when the resin thickness (liquid crystal polymer thickness) below the base plate is thinned in order to improve heat radiating performance, the resin becomes brittle and easy to break, however, increase in the strength is achieved by thickening the peripheral edge of the bottom of the case and accordingly, there is constituted the package having high reliability of mechanical strength.
(d) Since the air gap is present at an upper portion of the protective film, even when the protective film is expanded by heat, the expanded portion elongates only to the air gap portion and is not brought into contact with the cap on the upper side and accordingly, stress is not applied to the optical fiber by deforming the package and the optical fiber is difficult to break.